This invention relates to improvements in fluid heating equipment. It is especially concerned with improvements in electrical water heaters of the "instantaneous" type, i.e. heaters where the water is heated immediately before use as it passes through a container of small volume. Instantaneous water heaters have recently come into general use for hot showers, hand washers and other domestic appliances where relatively small flow rates are required.
Instantaneous water heaters need to be both safe and efficient. High wattage heaters up to 7 kW and above are employed to heat water as it passes through a small container, so that if for any reason the power remains connected to the heating element when the water cannot leave the container, as for example in closed outlet heaters, there is a risk that the container could rupture under the high pressure which can rapidly develop. A thermal cut-out or other temperature-related safety device is normally installed at the hottest part of the container to ensure that this cannot happen, but the presence of these cut-outs or other devices can lead to other problems associated with the operation of the heater, particularly where the element has a relatively high heat input.
Although cut-outs of rapid response can be provided, the heat stored in the element at the instant of cut-out may be sufficient to cause the temperature of the relatively small volume of water to rise significantly after the operation of the cut-out. If a cut-out responsive to a lower temperature is installed to overcome this problem, the water heater may be prone to what is known as "nuisance tripping" i.e. the thermal cut-out is triggered during normal use, or by a slight drop in the inlet water pressure.
It is an object of the invention to provide both an improved heating element and a container for housing said element for an instantaneous water heater, which significantly ameliorates the problems set out above.